A polymer having a hydroxyl group at both terminals is able to convert easily the hydroxyl group into other functional groups by carrying out a suitable reaction on the terminal hydroxyl group, and also, the polymer itself converts into a linear molecule and/or a network molecule by using reactivity of the terminal hydroxyl group and carrying out a suitable reaction on this hydroxyl group and, as a result, the polymer becomes a high-molecular weight compound having excellence in various properties such as strength, heat resistance, weather resistance, durability and so forth.
This polymer having a hydroxyl group at both terminals has, for example, the following great advantages 1 to 6 by displaying a feature such as having a hydroxyl group at both terminals.
1 In a case where the polymer is used as a raw material (a crosslinking agent and the like) for various kinds of resins such as a polyester resin, a polyurethane resin, a polycarbonate resin and the like, since there is not any unreacted material, all polymers are surely assembled in a resin-crosslinked structure. Therefore, various kinds of resins using the polymer does not show physical property-lowering derived from the unreacted material.
2 A polymer in which a functional group has been introduced into a side chain by copolymerizing a vinyl-based monomer having a functional group such as a hydroxyl group, a carboxyl group, an amino group and the like (hereinafter, abbreviated as "a copolymer of a functional group-containing vinyl-based monomer"); when said polymer is used for a reaction, its terminal becomes a play part (a free terminal) which is not assembled in the resin crosslinked) structure, but such a thing does not occur in a polymer having a hydroxyl group at both terminals.
3 Compared with the copolymer of a functional group-containing vinyl-based monomer, because scattering in the distance between the functional groups is very small, the distance between reacting sites (crosslinking sites) is nearly constant, so that a homogeneous resin (-crosslinked) structure is made.
4 In a case of a copolymer of a functional group-containing vinyl-based monomer, even if the synthesis of a thermoplastic polymer is attempted by making a material of 2.0 in the average number of functional groups and by allowing this to react with a chain-elongating agent having two functionalities, since a polymer having three or more functionalities is statistically included because of a reason originated from the synthetic process, a thermosetting polymer is obtained as the major part, and a thermoplastic polymer cannot be synthesized. However, in a case of a polymer having one hydroxyl group at each of both terminals and not containing a polymer having three or more functionalities, a thermoplastic polymer of which chain has been elongated can be easily synthesized.
5 In a case of a polymer having a hydroxyl group at both terminals and having at least two hydroxyl groups at one or more terminals, compared with a polymer having a hydroxyl group at both terminals, but only one hydroxyl group at the terminals, there is recognized an advantage that, because of increased crosslinking density, physical strength of a crosslinked matter can be elevated, and furthermore, reactivity of the terminal hydroxyl group can be elevated due to a synergistic effect of the terminal hydroxyl group.
6 In a case of using a polymer having a hydroxyl group at both terminals and having at least two hydroxyl groups at one or more terminals, in the use of a thermosetting-resin it is unnecessary to add either an expensive trifunctional isocyanate (NCO) compound or a polyol having three or more functionalities and displaying inferior handling performance, both of which are required in a case of curing a polymer having only one hydroxyl group at a terminal.
The polymer having a hydroxyl group at both terminals, by taking the above-described advantages, is very useful as a raw material or an additive for various resins such as a polyester resin, a polyurethane resin, a polycarbonate resin and the like and for various block polymers, and further, the polymer itself is very useful for uses such as a coating (a high solid coating, a low temperature curing coating, a water borne two-liquid type urethane coating, a water borne urethane coating, a powder coating and the like), an elastic wall material, waterproof for paint film, a pressure-sensitive adhesive, a floor material, a tackifier, an adhesive, binders (a magnetic recording medium, an ink binder, a casting binder, a burned brick binder, a graft material, a microcapsule, glass fiber sizing and the like), a sealant, urethane foam (hard, semihard, and soft type), urethane RIM, an UV-EB-curing resin, thermosetting type elastomer, microcellular, a fiber-processing agent, a plasticizer, a sound absorption material, a vibration-controlling material, a surfactant, a gel coat agent, a resin for artificial marble, an impact resistance-affording agent for artificial marble, a flexibility-affording agent for an epoxy resin and the like, a resin for ink, a film (a laminate adhesive, a protective film and the like), a resin, for laminated glass, a reactive diluent, various molding materials, elastic fiber, artificial leather, synthetic leather, a dispersing agent, an aqueous urethane emulsion and the like.
As the polymer having a hydroxyl group used hitherto for the above-mentioned uses are cited a copolymer of a vinyl-based monomer having a hydroxyl group on a side chain as well as a polyether, polyester, polybutadiene and polycarbonate having a hydroxyl group at a terminal and the like. However, first, since the copolymer of a vinyl-based monomer having a hydroxyl group on a side chain is prepared by a random type radical polymerization reaction between a monomer having a hydroxyl group and a monomer having no hydroxyl group, by-product formation of a copolymer having no hydroxyl group is difficult to suppress and, in order to avoid this formation, it is necessary to increase the hydroxyl group content in the copolymer and also, there is found scattering in the number of hydroxyl groups contained in one molecule. Because of this, in a case where a reaction is carried out between the copolymer of a vinyl-based monomer having a hydroxyl groups on a side chain and a polyfunctional compound capable of reacting with a hydroxyl group, a polymer showing sufficient stretching (processing performance for bending is excellent) and toughness is not obtained by reasons of remaining unreacted copolymer and large scattering in a distance between reaction sites, and by that a play chain part which does not directly participate in the structure of a crosslinked matter obtained after reaction is formed and a hydroxyl group not participating in the reaction remains. On the other hand, polyether, polyester, polybutadiene and the like having a hydroxyl group at a terminal, because they have a hydroxyl group at a polymer terminal, have a little defect which a copolymer of a vinyl-based monomer having a hydroxyl group on a side chain has. However, in a case of the polyether because of an ether bond on a main chain, in a case of the polyester because of an ester bond on a main chain, and in a case of the polybutadiene because of an unsaturated double bond on a main chain, these polymers have defects such as poor weather resistance, water resistance, heat resistance and the like.
As described above, at present, among polymers having a hydroxyl group, which are used as raw materials for the aforementioned uses, as additives for various resins and as raw materials for the resins there is not found any member satisfactory for all demands and capabilities such as toughness, stretching (processing performance for bending), weather resistance, water resistance, heat resistance and the like.
Although it is considered that a problem of this sort may be solved by a vinyl-based polymer having a hydroxyl group at both terminals, as mentioned below, the real situation is that any process for producing industrially a polymer having a hydroxyl group at both terminals from a wide range of vinyl-based monomers including polar vinyl-based monomers such as acrylic acid, an acrylic acid ester, methacrylic acid, a methacrylic acid ester and the like has not yet been established.
An example of a process for producing a vinyl-based polymer having a hydroxyl group at a terminal is a process such as introducing one hydroxyl group into one terminal of the polymer by using 2-mercaptoethanol and the like as chain-transfer agent and introducing another one (as an average) hydroxyl group into a polymer molecule by copolymerizing with 2-hydroxyethyl methacrylate and the like.
However, in this process, although two hydroxyl groups per one molecule of a polymer are introduced as average, only one of the two hydroxyl groups is introduced into one terminal of the polymer and another hydroxyl group is introduced not into the terminal, but into the middle of a main chain. Furthermore, since another one hydroxyl group is introduced by a copolymerization reaction, the total number of hydroxyl groups per one molecule of the polymer is in a scatter distribution such as being from one to three or more, and a wide distribution is seen in a distance between hydroxyl groups. Accordingly, an obtained polymer cannot almost display the aforementioned merit which the polymer having a hydroxyl group at both terminals has. Furthermore, because of adding a mercaptan compound, there are problems that the polymerization reaction becomes extremely slow, the polymerization conversion does not rise, and the smell of residual mercaptan remains.
Examples of a process for producing a vinyl-based polymer having a hydroxyl group at both terminals are, as shown in the undermentioned (i) to (iii), processes comprising carrying out a radical polymerization reaction of a vinyl-based monomer in the presence of various kinds of initiators and chain-transfer agents and the like.
(i) A process for producing a polymer having a hydroxyl group at both terminals by polymerizing styrene or butadiene by using an initiator having a hydroxyl group (refer to "Journal of Polymer Science", Part A1, Volume 9, p. 2029, published in 1971). PA1 (ii) A process for producing a polymer having a hydroxyl group at both terminals, comprising a thermal polymerization reaction or a photopolymerization reaction carried out by using a dithiocarbamate or thiuram disulfide, both of which have a hydroxyl group, as an initiator, or comprising a polymerization reaction carried out by using the dithiocarbamate or thiuram disulfide as a chain transfer agent and using hydrogen peroxide and the like as an initiator (refer to Japanese Official Patent Provisional Publication No. showa 61-271306). PA1 (iii) A process for producing a polymer having a hydroxyl group at both terminals, comprising a polymerization reaction carried out by using a disulfide, a trisulfide or the like having a hydroxyl group at both terminals as a chain transfer agent (refer to Japanese Official Patent Provisional Publication No. showa 54-47782.
However, the aforementioned conventional processes (i) to (iii) for producing a polymer having a hydroxyl group at both terminals have respective defects, as mentioned below, and it is not easy to synthesize a polymer having a hydroxyl group at both terminals surely, with a cheap price, simply and industrially from many kinds of vinyl-based monomers.
First, in the process (i), there is a problem that a usable vinyl-based monomer is limited to butadiene and styrene, and a polar vinyl-based monomer such as an acrylic acid ester, a methacrylic acid ester and the like cannot be used.
Next, in the process (ii), there is a problem that the thiuram disulfide having a functional group such as a hydroxyl group and the like is unstable and, thereby, its treating is difficult and also, a produced polymer is colored into yellow.
Finally, in the process (iii), there are the same problem as the aforementioned process (ii) and a problem that a flake of the initiator is introduced into a polymer terminal and a polymer having a hydroxyl group at only one terminal is formed as a by-product and, therefore, a polymer having terminal hydroxyl groups in a low number is formed.
As described above, at the present time there has not been established any process for producing industrially a polymer having a hydroxyl group at both terminals from a wide field of vinyl-based monomers including polar vinyl-based monomers such as acrylic acid, an acrylic acid ester, methacrylic acid, a methacrylic acid ester and the like.
Under these circumstances, it is an object of the present invention to provide a process by which a polymer having a hydroxyl group at both terminals can be easily obtained with a cheap price and good efficiency from a wide field of vinyl-based monomers including polar vinyl-based monomers such as acrylic acid, an acrylic acid ester, methacrylic acid, a methacrylic acid ester and the like.